Xkb provides a number of functions to allocate and free subcomponents
of a keyboard geometry. Use these functions to create or modify keyboard
geometries. Note that these functions merely allocate space for the new
element(s), and it is up to you to fill in the values explicitly in your
code. These allocation functions increase sz_* but never touch num_*
(unless there is an allocation failure, in which case they reset both
sz_* and num_* to zero). These functions return Success if they succeed,
BadAlloc if they are not able to allocate space, or BadValue if a parameter
is not as expected.

XkbAllocGeomSectionDoodads allocates num_needed
doodads and adds them to the specified section. No initialization of the
doodads is done.